Process instruments, such as used for sensing of process variables, for example, level or the like, include a sensing element and a control element. The sensing element may be, for example, a probe secured to and extending into a vessel or a non-contact element sensing from the top of the vessel. The control element is usually located in a housing. The housing may be physically secured to the probe or may be remotely located from the probe. In either case, the probe is electrically connected to the control element. The control housing includes electrical or electronic components used to sense a process variable. Some control electronics provide only local indication. Others transmit either a discrete on/off signal or a varying analog signal to remote control systems. In either case, electrical connections must be provided to the control electronics for power and/or signalling.
In some applications it is desirable to isolate customer accessible wiring for providing wiring to remote controls and/or power from the control electronics which is connected to the probe. One known type of transmitter uses a dual compartment housing comprising a cylindrical housing having a central circular wall separating the housing into two compartments. A control or electronics compartment of the housing is accessible from one side, while a wiring compartment is accessible from an opposite side of the housing. Such design prevents a user from accessing both compartments simultaneously. Also, depending on orientation, it may be difficult to obtain easy access to one or both compartments.
One particular type of process instrument comprises a microwave level sensing transmitter. Such a transmitter uses a probe which provides a high frequency transmission line positioned in the fluid. The probe is connected to control electronics in a control housing. Difficulties occur in impedance matching between the probe and the control electronics.
The present invention is directed to overcoming one or more of the problems discussed above in a novel and simple manner.